Frequency modulated radio relaying system



2 Sheets-Sheet 1 C. W. HANSELL FREQUENCY MODULATED RAD I 0 I RELAYING S i'S Tim I llllllll vvvvvvvv April 28; 1942.

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FREQUENCY MODULATED RADIO RELAYING SYSTEM Filed July 1, 1938 2 Sheets-Shet 2 POWER cor/mum use/114m 75 77 arms/e1:

l/ iy- 2 FHA 55 RFZA no DH'ECTOR INVENTORI CLARENCE IV IMMSEZL ATTORNEYS Patented Apr. 28, 1942 r 2,280,822 FREQUENCY MODULATED nanro RELAYING. SYSTEM Clarence W. Hansell, Port Jefferson, N. Y., assignor to-Radio Corporation of America, a corporation of Delaware Application July 1, 1938, Serial No. 216,872

27 Claims.

This application concerns a new and improved method of and means for relaying waves characteristic of any kind of signals known in the art today from one point to another. A particular application of my novel method and means is the relaying of frequency modulated facsimile signalsfrom one spaced point to another but the method is equally applicable to the relaying of telegraph, printer; telephone,- television and other kinds of signals.

By frequency modulated currents I mean currents whose frequency or phase is varied by modulation as distinguished from currents whose amplitude or strength is varied by modulation.

Although my invention was made as a result of study of radio relaying systems I realize that it is equally applicable to wire line and cable systems.

Relaying systems known in the art involve considerable apparatus such as amplifiers, frequency changers, modulators, demodulators, etc. This apparatus is expensive to provide and to keep in operation and its complexity and quantity tends to makeit subject to failures of many kinds. An ideal arrangement would be a radio frequency amplifying relay wherein the modulated wave to be relayed is intercepted, amplified and re-trans-' mitted without change in frequency. This ideal has not seemed to be readily obtainable at the present time due to known limitations of tubes, circuits, antennas, etc., which have prevented practical application of the method.

A purpose of my invention is. to provide as simple a system as possible where no frequency changes are necessary at the re-transmission points between the terminal stations. In this respect the present system differs from those known in the prior art wherein several frequency changing steps are accomplished. In the prior art the common practice has been to intercept a modulatedcarrier wave, demodulate it in a superheterodyne receiver and then to use the modulation energy to modulate the output of a radio transmitter operated at a new carrier wave frequency.

In the present invention I propose to obtain the above objects and others by the use of an as- In order to insure that my relaying system is at all times receptive to the wave to be relayed I have further provided a new and improved method and means for bringing the oscillating amplifier to the same frequency, or in tune with, the

wave to be relayed in case the frequency of the oscillator has deviated or drifted from its proper value or the frequency of the wave to be relayed has drifted. Additional means is provided for synchronizing the oscillating amplifier as to phase with the wave to be relayed. This re-tuning means includes synchronizing means for initially bringing the oscillating amplifier substantially to the same frequency as the received wave and additional means forautomatically adjusting and holding the oscillation of the oscillating amplifler substantially in constant phase relation with the received wave.

In one arrangement I use a phase rotation detector to accomplish the synchronizing or retuning of the oscillating amplifier to bring it into tune with the received wave.. This phase rotation detector ,or a separate one also supplie unidirectional currents to a reverse current relay to bring the oscillating amplifier in phase with the received wave.

' One serious and fundamental difilculty met in the prior art under certain circumstances is that caused by radio frequency feedback from output -.,,to input circuits of the radio frequency ampliher. 1 In practice a small amount of feedback from output to input circuits, perhaps by way of the antenna systems or connections will always exist. This feedback sets a limit upon the amplification which may be used in the amplifier without causing oscillation. Since it is desirable to make the amplification very large in order to cillating amplifier which oscillates continuously (due to .reaction or other causes) and entraining or synchronizing and controlling the frequency of the said amplifying oscillator by the wave to be relayed. and other wave relaying circuits will have no frequency changes such as were produced by heterodyning and modulation in the older systems.

be able to relay very weak received signals there is always a probability that oscillations may take place. In the present invention I contemplate employing so much amplification, in order to be able to relay weak signals, that oscillations will take place. I reduce the feedback to a very small amount in absolute value but it is unlikely that it will always be found practical with apparatus now used to reduce it to a value far below the level of the energy picked up from the distant trans-.

mitterwhose modulation is to be relayed. In fact I believe the energy fed back will often be much greater than the energy picked up from the distant transmitter. The more the absolute value The oscillating amplifier of the feedback is reduced, however, the greater will be the ability of the distant transmitter to control the frequency of the amplifier output. I

provide a repeater station with the lowest practiming or direction of rotation ing upon whether the I plifier oscillations is posed on the oscillation energy in the input circuit and used to control and modulate the exact frequency of the oscillations provided for reradiation or relaying.

Theory and experience prove that the frequency of any regenerative oscillating amplifier can always be controlled or synchronized by energy received from the distant transmitter over a certain band of frequencies, depending chiefly upon the relative strength of the received and locally fed back energies and upon the broadness of tuning of the radio frequency circuits asociated with the oscillating radio frequency amplifier. In obtaining a practical relay installation a fundamental problem is' to increase the frequency band over which the received energy can synchronize the amplifier oscillations.

In solving this problem effort was made to:

(1) Obtain the greatest and most constant reduction of energy fed back from output to input circuits.

(2) Make the frequency selectivity of the amplifier broad and as fiat as possible over the required frequency band. I

(3) Introduce devices for bringing the oscillations of the amplifier under the control of the received energy and for increasing the power of the received energy to synchronize and modulate the amplifier oscillations. 5

In operation of the relay 'one of the first problems is to bring the amplifier oscillations within the control of the received energy. Suppose, for

example, that there is sufiicient received energy to synchronize the amplifier oscillations over a band of only plus and minus 10,000 cycles. Then, when the system is started, it may be found that the amplifier oscillations are, say 20,000 cycles, oil

y from the frequency of the received energy and the received energy is therefore unable to control the amplifier oscillations. That is, the amplifier oscillations will not fall in step or synchronize with the received energy frequency.

Under this condition, if the amplifier input circuit has a detector associated with it, which detector may be first tubes in the amplifier system, or an intermediate stage, then from the detector I obtain beats at a frequency correspondceived energy and the amplifier oscillations. Furthermore, I use two detectors in which, by means of circuit tuning or otherwise, I provide for a difference in phase of energies at either the received frequency or the local oscillation fre-' quency, or both, to obtain from the detector two output beat frequency energies of like frequency but difierent phase. For example, for 90 relative phase shift in the potential and current of one of the radio frequency energies supplied to the two detectors, I obtain' ordinary 2 phase currents in the two detector outputs. The relative of the two phase currents is in one direction or the other dependfrequency of the local amabove or below the frequency of the received energy. This diiference in phase rotation is utilized to operate an automatic means for correcting the local oscillations to make them synchronize with the received energy as disclosed in my United States Patent #2,095,980 dated Qctober 19, 1937, and in ot e ing to the difference frequency between the reanodes.

.part of the input circuit related patents of G. L. 'Usselman and myself. The synchronizing system of my above patent has in practice proved effective both at Rocky Point and at Riverhead, Long Island.

To illustrate the principle of the invention of the present application I have attached hereto two schematic diagrams, illustrated in Figures 1 and 2 showing the essential elements of two radio relays each including phase detectors, oscillating amplifiers and frequency and phase control circuits arranged in accordance with my invention.

In Figure 1 I have shown an antenna or transmission line l8 corresponding to the arrangement of my United States application Serial #199,421 filed April 1, 1938, Patent No. 2,229,078, coupled to the input l2 and output M of a radio frequency amplifier. Preferably this radio amplifier includes means such as shielding, filtering, balancing, etc., for reducing feedback from the output I 4 to input l2 of the amplifier. In the modification illustrated balanced circuits are used as shown in the amplifier to assist in accomplishing the desired reduction of feedback. Moreover, where feasible the separate amplifier stages may be neutralized as shown. Obviously, any of the other well known elements and features of high frequency amplifiers well known in the art may be used.

In the amplifier of Figure 1 the first stage It comprises two amplifier and detector tubes 20 and 22 having their control grids coupled as shown to a tuned circuit 24 coupled to or forming l2. The anodes or output electrodes of the tubes 20 and 22 are connected with separate tuned circuits 26 and 28 respectively. For simplicity the electrode potential sources have been omitted and will not be described. The two amplifiers Hand 22 also serve as detectors, and may be tubes of any appropriate type such as screen grid tubes as shown, pentodes, or the type wherein secondaryelectron emission is made use of and so on.

Radio frequency output from the two tubes is passed from the circuits 26 and 28 to an oscillating amplifier l8, shown as a' single push-pull stage, but which may, in practice, comprise any number of stages, depending on the gain desired made up partly of energy from circuits 26, 28

and partly from feedback from othercircuits in the amplifier system. Also due to the oscillations produced in the amplifier by feedback, local oscillations are produced in the circuits associated with tubes 38 and 32 and energy of the local oscillations is induced by 34 back on the inductances 26 and 28 which are tuned above and below the natural frequency of operation of stage l8 by an amount 'sufiicient to produce "the phase displacement between the various voltages necessary to operate the frequency control circuits. The inductances may be de-tuned in opposite directions from the mean carrier frequency an amount such that the total phase displacement is, say, as in my patent referred to above.

Considering the first pair of tubes 20 and 22 as detectors they havelocal oscillations which may be of relatively high strength but with a phase difierence of, say 60 to 90, impressed upon their At the same time they receive energy from a'distant transmitter and this energy is impressed by 24 upon the control electrodes. I

There will, in practice, also be some locally generated energy reaching the control electrodes of 'tubes 20 and 22 which may be stronger than the received energy but I make its effect small as compared with the relatively strong local energy impressed upon the anodes of tubes 20 and 22.

In the arrangement shown the detectors 20 and 22 give a two phase beat frequency output which is reversed in direction of rotation when the local amplifier I8 is oscillating out of synchronism above or below the frequency of the received energy. The two phase energy is supplied to the primary windings of transformers 38 and 40 and is supplied by the secondary windings of said transformers to the windings 42 of a twophase motor relay having an armature action equivalent to that of a locked two-phase motor. The two-phase energy may, if desired, be amplifled in amplifiers 44 and 45. The relay will close one or the other of two contacts 48 and 50, depending upon the direction of rotation of the two phase. energy supplied to it. When unen'ergized the relay will hold both contacts open. A somewhat similar system for detecting phase and frequency differences and using the detected component to control the tune of a circuit is shown in my United States Patent #l,90'l,965.

Closing of one contact or the other will connect' a supply source to the winding 54 of the motor 52, energizing the field winding 54 of the small motor and causing said small motor 52 to rotate in one direction or the other to change the adjustments of the oscillating-amplifier l8 and bring it into synchronism with the received energy. The change in adjustment of the amplifier may be accomplished in various ways. For example, the motor 52 may drive the movable element of a tuning reactance such as a condenser 53 connected in the output circuit 36.

A phase rotation detector as described above has been described and claimed in G. L. Usselman's United States Patent #2,044,749 dated June 16, 1936, and in my United States Patent #2,104,801 dated January 11, 1938.

In practice, as the motor turns to vary the condenser the beat frequency between the re ceived carrier wave and the local oscillations will steadily decrease until a point is reached at which the received energy can synchronize the local oscillations. At this point the beat frequency will suddenly drop to zero andthe two phase output from the detectors will cease. However, at this pull away from exact synchronism with the received carrier, will unbalance the detector currents and this unbalance is used for operating a reverse current relay RR. which also controls the small motor 52 by controlling the positions. of contacts 55. Thus, we have a means of starting with local oscillations completely out of synchronism with the received energy and of automatically bringing the oscillations into synchronism followed by an almost exact optimum adjustment for maintaining synchronism.

Normal frequency modulation on the received wave energy used to transmit signals will cause instantaneous unbalances of the currents in the outputs of detectors 20 and 22 tending to make the relays vibrate but will not supply them currents to produce a steady state of unbalance in low resistance short circuited turn, is a very effective damper to prevent response to the useful modulation.

Mechanical damping may also be used.

As a further refinement I may increase the allowable modulation of the received frequency modulated energy by increasing the control of the received energy. To do so I propose to take some of the detector output currents or energy and apply it to frequency modulating tubes or devices coupled to the oscillating amplifier to modulate the frequency of the generated oscillation. The phase or polarity of the currents supplied from the detectors to the modulators will point synchronism may still be lost easily and r be so chosen that its effect upon the amplifier oscillations is to make them follow the received frequency modulation more closely. I That is, the input to the modulators is in such phase as to reduce itself by removing or reducing phase lag in the response of the oscillations to the received frequency modulated energy. Anarrangement including these ure 2.

In Figure 2 the detectors 2!! and 22 detect the phase displacement between the received wave applied at l I and thelocal oscillations impressed from the inductance 33 of tuned circuit 34 on the off-tuned circuits 26 and 28. The detected currents which are characteristic of the modulations on the received wave are supplied from the outputs of 20 and 22 to radio frequency suppressing fllter circuits 35 and from 35 to alternating current amplifiers 58 and 3| wherein they are amplified the desired amount. The amplified currents are supplied to the control grids of tubes 63 and 65. The anodes of tubes 63 and 65v are connected to tuned circuits 61, 69 respectively. These circuits are tuned one above and the'other below .the mean frequency of the features has been shown in Figoscillatory energy-to be produced in the oscil gaiting ampliflerincluding tubes 30 and 32, circuit e c. circuit 61 is coupled to the output circuit 33 of tubes 30, 32 as is a reactance 13 forming a part of tuned circuit 69.

In operation the phase rotation detectors 20, 22 operate as in the prior modification todetect phase shifts or variations or displacements between the received wave and the oscillations supplied from the oscillating amplifier tubes 30 and 32 to the anodes of the detector tubes 20, 22. These modulation components obtained in the output of the phase relation detector tubes 20 and 22 include in addition to direct currents characteristic of mean frequency shifts and phase A reactance ll formi g Dart of tuned 59, 6| and control differentially the conductance tained from the .outputs of tubesof tubes 63, 65 to thereby control the effectiveness ofthe tuned reactances 61, 69 to control the tuning of circuit 36. By this means the incoming waves are given increased control of the frequency of the oscillations of tubes 30, 32. The

input to the modulators 63, 65 is in such phase as to reduce itself by removing or reducing phase lag in the response of the oscillating amplifier to the received frequency modulated energy.

One result of this increased control of the receivedenergy in controlling the frequency of the local oscillations is to reduce modulation distortions of the repeated frequency modulated currents or waves which might tend to take place in the repeater due to phase lags. The circuits including amplifiers 59 and 6|, and tubes '53 and 65, etc,, supply the modulating effects in proper phase. to the circuit 36 and if the phases of the modulating effects as supplied are opposed, this can be corrected by reversing the leads or connections of the modulator circuit. The currents supplied at 59, 6| are also detected in the phase rotation detector 15 to produce uni-directional currents which, as in the prior figure, control a reversible motor 19 which may be similar to the reversible motor 52, 54 of Figure 1. Phase rotation detectors suitable for use as detector 15 have been described in prior patents referred to.

If desired, in a modification, the electromagnetic coupling between inductances 26, 2B and 33 may be omitted so that radio-frequency output from tubes 20, 22, appearing in circuits 26, 28, will exert substantially no synchronizing effect upon oscillations produced by tubes 30, 32 and their associated circuits. In this case output circuit radio-frequency power from coil l4 via antennas and transmission lines, appearing in input I, may provide heterodyning energy to beat with received currents in the circuits of tubes 20, 22. In this case the high frequency oscillator, comprising tubes 30, 32 is controlled as to mean frequency by phase rotation variations in the outputs of amplifiers 59, 6| and E modulated in frequency in accordance with the modulation components obtained by demodulating the frequency modulated waves in detectors 20, 22. In other words, tubes 20, 22 may serve only as detectors and not-as high frequency amplifiers if the input is coupled directly to the circuits of tubes 30, 32. g

i A reversed current relay similar to RR of Figurs 1 actuated by uni-directional currents ob- 20 and 22 may be incorporated in the modification of Figure 2 and supplement the action of the phase rotation detector 15 and its relay and the action of the frequency modulator including tubes 63 and 65..

By this means .of control through -a phase modulation or phase difference detector and a frequency modulator, or phase modulator, it is possible to synchronously modulate a powerful or their alternatives, may then q the frequency of the relay transmitter witha relatively minute received frequency modulated signal. of course, amplification may be used between the detector and the modulator and the more amplification "tubes now available.

serve the whole purpose of bringing the relayoscillations into synchronism and making them follow the modulation. This would have the advantage of eliminating all mechanically moving parts such as the relays including 11 and the motor 19. This control through the phase or frequency modulators may be used with the coupling at 26, 28 and 33 or alone.

One advantage of the detector-modulator controlled relay, under present conditions, is that it may be used to relay frequency modulated waves whose carrier frequency is so high that little if any amplification is obtainable with The use of one detector, one modulator and a, modulation frequencyamplifier between them. would be far simpler than some prior relaying systems and would eliminate a considerable part of the cost of manufacture and installatio improve reliability, reduce maintenance cost, and save frequency space by placing a chain of relays all on one frequency.

Another modification is that the amplifiers 30, 32 of Figures 1 and 2 may be simply rather low power intermediate frequency amplifiers in a chain of amplifiers. That is, there may be additional stages of amplifier, after tubes 30, 32 to provide the final output from the repeater. This modification is likely to be used 'in practice because the control circuits of Figures 1 and 2, be standardized units of rather low power level which may be associated with various amounts of amplification, in following amplifiers, to suit particular circuit requirements.

Monitoring of the modulation is carried out by simple addition of a modulation frequency amplifier or, if desired, by tapping off some energy from the controlling amplifier, say at 59 and 6|. Frequency selectivity to prevent interference from outside the band assigned to the relay may be obtained by means of a simple low pass filter, not shown, between the detector and frequency modulator. Considerable air is, of course, also obtained from antenna directivity and frequency selectivity and from radio fre-.

quency circuit selectivit I claim:

1. A repeater of frequency modulated currents comprising an oscillator operating substantially at the frequency of the modulated current, curexcited by said currents, and means controlled by said amplifying means for holding the oscillator frequency of operation equal to the frequency of the repeated currents.

2. A repeater of received frequency modulated currents comprising an oscillator operating substantially at the frequency of the received currents, means coupling said oscillator with transmitting means, and 7 means for automatically bringing the frequency of the oscillator toward received currents to establish synchronism between received and transmitted currents.

. 3. A repeater of received frequency modulated currents comprising an oscillator, means for automatically bringing the oscillator into synchronism with said received currents, and means for automatically bringing the oscillator into a fixed received currents.

and substantially fixed phase relation with the said received currents, and means for deriving energy corresponding-to frequency modulations on the received current and for utilizing this energy to modulate the produced currents substantially in accordance with modulations of the received current.

5. In a relay system a frequency modulated wave detector, means for impressing received frequency modulated wave energy thereon, an

oscillator operating at the frequency of said received wave coupled thereto to be entrained thereby, means for synchronizing said oscillator in accordance with the frequency of the wave energy impressed on said detector and a translating circuit coupled with said oscillator.

6. In'a relay system, a frequency modulated wave detector, means for impressing frequency modulated wave energy thereon; an oscillator coupled thereto, means for synchronizing said oscillator in accordance with the mean frequency of the wave energy impressed on'said detector and means for modulating the frequency of the oscillations produced by said oscillator in accordance with the output of said detector.

7. In a relay system, a frequency modulated wave detector, means for impressing frequency modulated wave energy thereon, an oscillator coupled thereto and entrained thereby, means for synchronizing said oscillator in accordance with the mean frequency of the wave energy impressed on said detector and means for synchronizing the phase of the oscillations generated by said oscillator, in accordance with the phase of said waveenergy impressed on said detector.

8. In a signalling system, an oscillator arranged to oscillate continuously, a translating circuit coupled thereto, means for receiving frequency modulated wave energy, means for entraining said oscillator with said received frequency modulated wave energy as to frequency, supplemental means for entraining said oscilla- I means for bringing said oscillator into phase with said received wave, and means for modulating the frequency of the oscillations produced by said tor'with said received frequency modulatedenergy as to phase, and means for modulating the oscillations produced by said oscillator in accordance with modulations on said wave energy.

9. In a signalling system, an oscillator arranged to oscillate continuously, a translating circuit coupled thereto, means for receiving frequency modulated wave energy, means for en-:

training said oscillator with said received frequency modulated wave energy as to frequency, and supplemental means for entraining said oscillator with said received frequency modulated wave energy as to phase.

10. In a relaying system, an oscillator of the balanced neutralized type adapted to produce oscillations continuously and transmit the same, and means for impressing on said transmitted oscillations frequency variations corresponding to frequency variations at signal frequency on a received wave comprising means for bringing said oscillator in tune with said received wave, and means for bringing said oscillator into phase with said received wave.

11. In a relaying system, an oscillator of the balanced neutralized type adapted to produce oscillations continuously and transmit the same,

and means for impressing on said transmitted oscillations frequency variations corresponding to frequency variations at signal frequency on oscillator in accordance with modulations on said received wave.

13. In a relay system, a frequency modulated wave detector having an input circuit energized by frequency modulated wave energy modulations on which are to be relayed, said detector having an output, an oscillator coupled to said detector to derive energy therefrom and impress energy thereon, a translating circuit coupled with said oscillator and means coupled with said detector for detecting phase displacement between energy supplied to said detector from said oscillator and wave energy impressed on the input of said detector, and means for controlling the tuning of said oscillator in accordance with the currents obtained by detecting said phase relation.

14. In a frequency modulated wave relaying system, a pair of electron discharge devices, each having input electrodes and output electrodes,

alternating current circuits including tuningmeans connecting the electrodes of said discharge devices in oscillation producing circuits wherein continuous oscillations are produced, a pair of spectively, the mean frequency of the oscillations generated in said first named tubes and circuits, means for coupling said tuned circuits to circuits of said first named tubes to derive therefrom exciting voltages, means for impressing frequency modulated wave energy on the input electrodes of said detector tubes, a pair of alternating current amplifiers coupled differentially with the output electrodes of said detector tubes, a relay coupled with said alternating current amplifier, a reversible motor associated with the tuning means in the alternating current circuits connected with said first named pair of tubes, and a coupling between said relay and said reversible motor.

15. In a frequency modulated wave relaying system, a pair of electron discharge devices, each having input electrodes and output electrodes, alternating current circuits including tuning means interconnecting the electrodes of said dis charge-devices in oscillation producing circuits, means for energizing the electrodes of said tubes to produce in said tubes and circuits continuous oscillations, a pair of electron discharge detector tubes each' having input and output electrodes, alternating current circuits connected with output electrodes of each of said detector tubes,

system, a pair of electron discharge devices, each having input electrodes and output electrodes, alternating current circuits including tuning means interconnecting the electrodes of said discharge devices in oscillation producing circuits, a pair, of electron discharge detector tubes each having input and output electrodes, alternating current circuits connected with output electrodes of each of said detector tubes, means for tuning said alternating current circuits above and below respectively, the mean frequency of the oscillations generated in said first named tubes and circuits, means for coupling said tuned circuits to circuits of said first named tubes, means for impressing frequency modulated wave energy difierentially on the input electrodes of said detector tubes, a pair of alternating current amplifiers coupled differentially with the output electrodes of said detector tubes, and means energized by potentials from the outputs of said amplifiers for modulating the oscillations produced by said devices and circuits. I

17. In a relaying system, an amplifying oscillator comprising a pair. of electron discharge devices having input and output electrodes connected differentially in oscillation generating circuit, a frequency modulated wave detector having input electrodes excited by frequency modulated wave energy to be relayed and having output electrodes, a wave frequency modulator comprising a pair of modulator tubes having input elecducing oscillations of a mean tially equal to the mean frequency of said freproduced oscillations as to frequency and phase with said wave energy by means of said produced potentials.

, 20. The method of relaying high frequency wave energy modulated in frequency at signal frequency without changing substantially the mean frequency of the wave energy during said relaying process which includes the steps of, producing oscillations of a mean frequency substantially equal to the mean frequency of said frequency modulated wave energy, beating said produced oscillations with said wave energy and rectifying the resultant beat note, and modulating the frequency of the entrained oscillations in accordance with the rectified resultant.

21. The method of relaying high frequency wave energy modulated in frequency at signal frequency without changing substantially the mean frequency of the wave energy during said relaying process which includes. the steps of, profrequency substanquency modulated wave ener beating said produced oscillations with said wave energy to produce a resultant beat note, rectifying said resultant beat note to produce potentials characteristic coupling between said last named circuit and said trodes coupled with the output-electrodes of said frequency modulated wave detector and reactances coupling the outputelectrodes of said modulator tubes to circuits of said oscillating amphfier tubes to control the tuning of said circuits and thereby control the frequency of the oscillations generated therein.

18. The method of relaying high frequency wave energy modulated in frequency at signal frequency without changing substantially the mean frequency of the wave energy during said relaying process which includes the steps of, producing oscillations of a mean frequency substantially equal to the mean frequency of said frequency modulated wave energy, entraining said produced oscillations by said wave energy, and I modulating the entrained oscillations in accordance with the frequency modulations onsaid wave energy.

19. The method of relaying high frequency wave energy modulated in frequency at signal frequency without changing substantially the mean frequency of the wave energy during said relaying proces which includes the'steps of, producing oscillations of a mean frequency substan tially equal to quency modulated wave produced oscillations by said wave energy, producing potentials characteristic of the modulations on said wave energy and synchronizing said the mean frequency of said fresaid oscillation generator energy, entraining said erator including an electron discharge of the modulations on said wave energy and synchronizing said produced oscillations as to frequency and phase with of said produced potentials.

22. In a signaling system, an oscillation generator arranged to generate wave energy of controllable frequency, said generator including. a tuned frequency controlling circuit, a translating circuit coupled to said tuned circuit, a circuit for receiving frequency modulated wave energy, a

oscillation generator for quency modulated wave energy on said oscillation generator to entrain the frequency of operation of the sameby said received frequency modulated wave energy, connections for deriving potentials corresponding to frequency modulations on said received wave energy, and control circuits responsive to said derived potentials for controlling the tuning of said tuned circuit to assist in. entraining said generator.

23. In a .signaling system, an oscillation gendevice impressing received frecoupling between said receiving means and the input electrodes of the device of said oscillation generator for entraining said oscillation generator by said received frequency modulated wave energy, and means including a rectifier controlled by the modulations on said received wave energy for varying the tuning of said tuned circuit to also entrain said oscillation generator.

24. In a signaling system, an oscillation generator including an electron discharge device having input eiectrodes and having output electrodes coupled to a tuned circuit,

amplifying circuits and the input electrodes of for entraining said oscillation generator with said received frequency modulated wave energy, and additional means controlled by the modulations on said received wave energy for varying the tuning of said tuned said wave energy by means,

up and amplifying frequency modulated wave energy, a coupling between said circuit to further entrain said oscillation generator.

25. In a signaling system, an oscillation generator of the electron discharge tube type having electrodes coupled in oscillation generating circuits including a tuned circuit, a translating circuit coupled to said tuned circuit, a circuit for receiving frequency modulated wave energy, a coupling between said last named circuit and said oscillation generating circuits for impressing received frequency modulated wave energy on said oscillation generator to entrain the same, an electron discharge device system having a control electrode and having output electrodes coupled to said tuned circuit to control the tuning thereof, and connections for impressing potentials, which vary in accordance with modulations on said received wave energy, on the control electrodeof said electron discharge device system to thereby'control the tuning of said tuned circuit.

,26. In a signaling system, an oscillation generator of the electron discharge tube type having electrodes regeneratively coupled in oscillation generating circuits including a tuned circuit, a

translating circuit-coupled to said tuned circuit,

a circuit for receiving and amplifying frequency modulated wave energy, a coupling between said last named circuit and said oscillation generating circuits for impressing received frequency modulated wave energy on said oscillation generator to entrain the same by said received frequency modulated wave energy, an electron discharge tube system having a control electrode and having output electrodes coupled to' said tuned circuit to control the tuning thereof, and connections for impressing potentials which vary in accordance with frequency modulations on said received wave energy on the control electrode of said electron discharge tube system to thereby control the tuning of said tuned circuit.

27. In a frequency modulation signaling system, an oscillation generator arranged to oscillate continuously, a translating circuit coupled to said generator, a, pick-up circuit for receiving frequency modulated wave energy, a circuit amplifying the picked up wave energy, means coupling said amplifying circuit to said oscillation generator for entraining and thereby controlling the frequency of the waves generated by said oscillation generator with said amplified frequency modulated wave energy, a supplemental circuit responsive to frequency changes in the received waves to produce relatively low frequency currents representative of said changes, and apparatus utilizing said produced low frequency currents to additionally control the waves generated by said oscillation generator.

CLARENCE W. HANSELL. 

